The present invention contemplates an improved method and apparatus for abatement of gasoline vapor emissions at a service station or any location where liquid gasoline is transferred from one container or tank to another and particularly relates to certain modifications, improvements, and additional safety features in the apparatus and method of abatement of vapor emissions as described in U.S. Pat. Nos. 4,009,985 and 4,118,170 owned by a common assignee. The patents describe service station vapor emission conditions in detail and such description and subject matter of said patents are incorporated herein by reference.
Generally speaking, these patents disclose an apparatus and method for controlling vapor emissions wherein the system preferably operates under a slight vacuum, arranged to permit collected gasoline vapors in the system to recondense in the underground storage containers, provides equilibrium or saturated vapors to blanket the stored liquid gasoline from air thus preventing further evaporation of gasoline, provides vapors to replace gasoline dispensed, suppresses the formation of excess vapors, and thermally oxidizes any excess vapors in the system into carbon dioxide and water vapor which are clean, odorless, invisible and nonpolluting. Such patents disclose multistage burners for disposing of the vapors, each burner being adapted to operate under certain specified conditions.
Generally speaking, excess gasoline vapors at a gasoline service station may occur as a result of diurnal conditions; that is, breathing vapor losses caused by alternate expansion and contraction of storage container contents due to day and night temperature and pressure differentials. During transfer of liquid gasoline to or from a vehicle tank and storage container, displacement losses occur upon refilling a partially empty or empty storage tank which may normally expel an equivalent volume of vapor through the vent pipe of the storage container. Further, when an automobile tank is filled with fresh gasoline, more gasoline vapors are produced as gasoline is dispensed. The volume of vapors discharged from a vehicle tank during such refueling may be from 2% to 15% greater than the liquid volume of the gasoline dispensed.
Further, in some prior proposed emission control systems, a slight vacuum may be present at the gasoline pump dispensing nozzle which may be provided sealing relation with the fill pipe of the vehicle tank; and within the remainder of the system such as the storage tanks, vent line and disposal means, a blower system is employed to move the vapors to the disposal means under positive pressure. In such prior proposed system, there may be considerable pressure variation as from for example, 3" to 20" of water column. As a result, operation of the burner means at the disposal means is nonuniform and consistently complete burning of the vapors is not always achieved.
In another prior proposed vapor emission control system, known as the "balance" system, efficient operation of the system is affected by variable hot and cold conditions which cause difficulty in maintaining the balance required to meet the emission control standards.
Further, each gasoline service station is characterized by its own particular installation in that the distances between the gasoline dispensing pumps and the gasoline underground storage containers and also the distance to the disposal means creates a vapor system in which the pressure condition throughout the entire system may vary in terms of pressure drop in the vapor conducting lines. In the prior proposed system which includes the use of positive pressure to move vapors along a vapor conducting line to a disposal means, the presence of slight leaks anywhere along such system is not only hazardous, but also further affects the pressure variations in the system. There may be other features about a particular service station installation which may unfavorably affect the operation and efficiency of a vapor emission control system.